Photographic processes using silver halide have been most widely used in the past due to their excellent photographic properties such as sensitivity or control of gradation, etc., as compared with other photographic processes, such as an electrophotographic process or a diazo photographic process. In recent years, with respect to image formation processes for light-sensitive materials using silver halide, many techniques capable of easily and quickly obtaining images have been developed by changing the conventional wet process using a developing solution into a dry development process such as a process using heat, etc.
Heat developable light-sensitive materials are known in the field of these techniques. Heat developable light-sensitive materials and processes therefor have been described, for example, in Shashin Kogaku no Kiso (The Foundation of Photographic Technology), pages 553 to 555 (published by Corona Co., 1979), Eizo Jyoho, page 40 (April, 1978), Nebletts Handbook of Photography and Reprography, 7th Ed., pages 32 to 33 (Van Nostrand Reinhold Company), U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, No. 17029, pages 9 to 15 (June, 1978).
Many different processes for obtaining color images have been proposed. With respect to processes for forming color images by the reaction of an oxidation product of a developing agent with a coupler, it has been proposed to use a p-phenylenediamine type reducing agent and a phenolic coupler or an active methylene coupler as described in U.S. Pat. No. 3,531,286, a p-aminophenol type reducing agent as described in U.S. Pat. No. 3,761,270, a sulfonamidophenol type reducing agent as described in Belgian Pat. No. 802,519 and Research Disclosure No. 137 (RD-13742), pages 31 and 32 (September, 1975) and the combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler as described in U.S. Pat. No. 4,021,240.
Also, processes for forming a positive color image by a light-sensitive silver dye bleach process, with useful dyes and methods for bleaching have been described, for example, in Research Disclosure, No. 14433, pages 30 to 32 (April, 1976), ibid., No. 15227, pages 14 and 15 (December, 1976) and U.S. Pat. No. 4,235,957, etc.
Further, processes for forming images upon heat development utilizing compounds originally having a dye moiety and capable of releasing a mobile dye in correspondence or counter-correspondence to the reduction reaction of silver halide to silver under conditions of high temperature have been described, for example, in European Patent Applications 76,492A and 79,056A, Japanese Patent Application (OPI) Nos. 28928/83 and 26008/83, etc.
In such image forming processes, it is usual for a base or base precursor to be present in a light-sensitive material at the time of heating for the purpose of accelerating development. However, an attempt to combine a base or a base precursor and a silver halide emulsion spectrally sensitized with a sensitizing dye in a light-sensitive material has suffered from the defect that a decrease in sensitivity occurs during preservation prior to use. Therefore, it is generally not easy to improve the developing property and preservability prior to use while maintaining the sensitivity of the light-sensitive material.
The inventors have previously found that the above-described defect can be eliminated by employing a silver halide emulsion which comprises silver halide grains prepared in the presence of a sensitizing dye as described in U.S. patent application Ser. No. 697,988. However, since this method has a tendency to increase in fog, further improvement has been desired.